This invention generally concerns inkjet printers, and is specifically concerned with a multiple-head inkjet printer for use in a photographic mini-lab that is capable of producing either separate adjacent images or a single image across the width of a printing medium.
Photographic mini-labs capable of rapidly providing photographic prints from color film are well known in the prior art. However, because of the cost of the silver halide paper and chemicals that such photographic prints are based upon, the resulting prints are relatively expensive on a per area basis compared with image prints produced by color inkjet printers which use relatively inexpensive inks and papers. Additionally, inkjet printing processes are inherently faster than photographic printing process since they do not require time consuming chemical development steps. As the cost of inkjet printers drops and the quality of the resulting printed images improves, there is a growing interest in the development of mini-labs capable of producing photographic-quality prints from such printers. Such a printer-based mini-lab would have the added advantage of providing the consumer with a number of image modification options which are either unavailable or impractical in the context of a silver-halide based mini-lab. For example, the originally-captured digital image could be displayed on a computer monitor prior to printing to allow the consumer to crop, blow up, vignette, shade, or reduce some or part of the image. The overall color tint and intensity of the image could be easily controlled and selected in much the same manner that the tint and color intensity of a color television is adjusted. However, in order for such a digitally controlled, inkjet-type mini lab to be commercially desirable, it must also be capable of rapidly producing prints of different sizes (i.e., 4xc3x976, 6xc3x978, 8xc3x9710 inch prints, etc.). Since the orifice plate of a typical commercially available inkjet printhead is, at most, only about 1 inch long and includes a maximum of only about 1000 inkjet orifices, the use of a plurality of printheads is necessary to obtain a high production rate.
While it is not difficult in principal to coordinate a plurality of such printheads to print multiple adjacent images across a printing medium (such as, for example, two or three adjacent 4xc3x976 images), problems arise when such a multiple array of printheads are coordinated to print larger images. For example, if one attempts to construct an end-to-end abutment of the nozzle plates of several printheads to form the equivalent of a single large printhead, mechanical interference between the edges of the printheads make such an abutted configuration impractical, if not impossible. Alternatively, several printheads could be overlapped in a staggered configuration such that their respective orifice plates are aligned along an axis transverse to the printing medium. However, such a staggered alignment must be done to tolerances of at least {fraction (1/1000)} of an inch in order to avoid the creation of line-shaped printing errors between the printheads which are readily detectable by the human eye. And even if such mechanical alignment were achieved, linear printing errors can also occur as a result of slight angular misalignments between the staggered array of printing heads and the printing medium as it is continuously moved relative to the printheads during the printing operation. Finally, the digital imaging and control circuitry necessary to implement the production of a single, integrated image from a multiple array of printheads is relatively complex and hence more apt to generate imaging errors. Of course, all of the aforementioned problems could be obviated by the creation of a printhead whose orifice plate was as wide as the printing medium moved beneath it. Unfortunately, it is difficult to manufacture orifice plates more than approximately 1 inch long without the introduction of small misalignments of the inkjets along the longitudinal axis of the plate which in turn could produce perceptible imaging errors.
Clearly, there is a need for a multiple-head inkjet printer that is capable of producing photographic-quality color images on a printing medium in a variety of sizes without the introduction of linear imaging errors and without the need for high-precision mechanical alignments between the printheads and the printing medium. Preferably, such a printer could be assembled largely from inexpensive and commercially available printheads. Ideally, such a printer could be operated by way of simple, reliable and inexpensive printing circuitry.
Generally speaking, the invention is a multiple-head inkjet printer that eliminates or at least ameliorates all of the aforementioned shortcomings associated with the prior art. The inkjet printer comprises a carriage having an axis traversing a printing medium, a plurality of inkjet printheads axially movable along the carriage and spaced apart from one another, each printhead being capable of independently printing a separate image on the printing medium, and a printhead driver assembly for simultaneously moving each of the printheads along the carriage equal axial distances while maintaining a spacing distance between the printheads.
The carriage has a length along its axis sufficiently greater than the width of the printing medium to allow a single one of the printheads to print a single image that extends completely across the printing medium. Hence, in one mode of operation, the plurality of inkjet printheads can simultaneously print adjacent, independent images across the width of the printing medium. In another mode of operation, a single printhead may print a single relatively large image completely across the width of the printing medium, thus avoiding the problems associated with printing a single image with multiple printheads. Of course, an intermediate mode of operation is also possible wherein less than all of the plurality of inkjet printheads are used to print fewer but larger images across the width of the printing medium.
In the preferred embodiment, the inkjet printer includes a rotatably mounted carrier drum for moving the printing medium across the transverse axis of the carriage. The width of the printing medium is preferably the same or slightly greater than the width of the carrier drum so that the edges of the medium are even with or overlap the edges of the drum. Such a configuration avoids the spraying of ink from the printheads onto the edges of the carrier drum.
The printhead driver assembly may include a lead screw threadedly engaged to each of the plurality of inkjet printheads in combination with a reversible stepper motor. The output shaft of the stepper motor is preferably engaged to the lead screw via a gear train. The motor driven lead screw serves to slidably drive the plurality of inkjet printheads back and forth across the carriage in shuttle fashion during a printing operation, while maintaining the same spacing distances between adjacent printheads.
The inkjet printer may also include caps detachably connectable over the inkjet nozzles of printheads which are not used in a printing operation where fewer than all of the printheads are used to simultaneously print one or more images across the width of the printing medium. Alternatively, the control circuit of the printer assembly may be programmed so that ink droplets are expelled from the nozzles of such unused printheads whenever these printheads are slidably moved away from the printing medium during such a printing operation. In either case, problems are avoided which might otherwise occur if ink were allowed to dry in the inkjet orifices of the printhead not used during such a mode of operation.